<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
    .box{
        height: 200px;
        width: 200px;
        background:yellow;
        position: relative;
        margin: 0 auto;
    }
    .child{
        height: 100px;
        width: 100px;
        background:red;
        position: absolute;
        top: 10px;
        left: 10px;
        z-index: -1;
    }
    .b1{
        width: 200px;
        height: 200px;
        background-color: red;
        position: absolute;
        top: 100px;
        left: 100px;
        z-index: 1;
    }
    .b2{
        width: 200px;
        height: 200px;
        background-color: yellow;
        position: absolute;
        top: 0px;
        left: 0px;
    }
</style>
</head>
<body>
    <div class="box">
        <div class="child"></div>
    </div>
    <div class="b1"></div>
    <div class="b2"></div>
</body>
</html>